Aminoglycoside antibiotics have been commonly used as a medical treatment against infectious diseases for over 60 years, although the prevalence of aminoglycoside resistant bacteria has significantly reduced their effectiveness. Aminoglycosides have two or more amino sugars bound to an aminocyclitol ring through glycosidic bonds. Naturally occurring aminoglycosides (produced by Actinomycetes) are widely used as antibiotics against bacterial infections of animals and humans. These include the well-known antibiotics kanamycin, streptomycin and neomycin. Aminoglycoside antibiotics are believed to act on the bacterial protein synthesis machinery, leading to the formation of defective cell proteins.
In medicine, fungal diseases have emerged over the last 25 years as a major public health problem. Among the prominent reasons for this increase are the lack of efficacious antifungal agents, increases in immunocompromised conditions (e.g., organ transplants and HIV/AIDS), and widespread resistance to the most commonly used antifungals. The strongest medically used antifungal agent, amphotericin B, is an effective medication, but is also highly toxic to patients. The toxicity levels of the available antifungal medications are a common concern for medical practitioners. U.S. Pat. No. 5,039,666 to Novick, Jr. (1991) shows an aminoglycoside compound “gentamicin” having reduced nephrotoxicity induced by the aminoglycoside. Other common antifungal medications are used to treat infections such as athlete's foot, ringworm, candidiasis (thrush) and serious systemic infections such as cryptococcal meningitis, and others.
In agriculture, the control of crop diseases by direct application of biocides remains the most effective and most widely used strategy. Nevertheless, concerns with inconsistent and declining effectiveness, environmental impacts, animal/human toxicity, and costs continue to challenge the use of existing biocides. Traditionally, aminoglycosides have been developed and used as antibiotics against bacteria. A recent report, however, suggests inhibition of plant pathogenic fungi (particularly by paramomycin) by traditional and natural aminoglycosides. One specific example of a crop pathogen is Fusarium graminearum, the most common causative agent of head blight disease in wheat and barley in North America. Infection with F. graminearum is difficult to predict and can result in catastrophic crop loss.
Kanamycin is a known aminoglycoside antibiotic. The antibiotic function of kanamycin is believed to be related to its ability to affect the 30S ribosomal subunit of bacteria, causing frameshift mutations or preventing the translation of RNA. Either frameshift mutations or a lack of RNA translation can lead to a reduction or absence of bacterial protein synthesis and, ultimately, to bacterial death. Unfortunately, kanamycin has been rendered all but obsolete for clinical use due to the emergence of resistant bacteria.
Clearly there exists a need for novel antimicrobials to address the problems of resistant bacteria and fungi, both in human medicine and in crop disease. There is also a clear need for novel antimicrobials, especially antifungals, with reduced toxicity. Furthermore, it would be desirable for new antimicrobial compounds to be selective against either bacteria or fungi, so treatment for one of either bacterial or fungal disease does not contribute to the buildup of antimicrobial resistance in the other. Selective antimicrobial activity is especially desirable for antifungals used to treat crop disease, such as Fusarium head blight, due to the possibly large amounts of antimicrobial agent released into the environment when crops are treated. The present invention provides for novel aminoglycoside antimicrobials that are effective, have relatively low levels of toxicity, and are selective against fungal pathogens.